1. Field of the Invention
The present invention relates to a method and an apparatus for spraying a release agent in a die casting machine, and more particularly to a method and an apparatus for spraying a release agent onto a die cavity surface in a die casting machine which employs a servo motor-driven, electrically-powered die clamping apparatus capable of positioning a movable die plate at any position in die opening/closing directions.
2. Background Art
A technique for spraying a release agent or a heat retaining agent (hereinafter referred to simply as a release agent) onto a metal cavity surface in a die casting machine is known, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 9-182946. The patent publication describes provision of a spray head having spray nozzles, which is movable in the die opening/closing directions of a die consisting of a movable die and a fixed die. A stand-by position of the spray head is set at a position from which the spray head can approach a position between the movable die and the fixed die when the dies are open.
The spray head is designed to move in the die opening/closing directions according to the thicknesses of the movable and fixed dies and also move to or approach a position between the movable and fixed dies. Spraying after the approach of the spray head is required to be carried out with an appropriate spray distance between the spray head and the die cavity surface of each die. In case of an inappropriate spray distance, a release agent would be sprayed from the spray head in a relatively large amount onto one cavity surface, whereas the release agent would be sprayed in a relatively small amount onto the other cavity surface.
In such a conventional spray apparatus for a release agent, the setting of a spray distances to each of fixed and movable dies is generally practiced by moving a spray head in the die opening or closing direction when the dies are open so as to position the spray head at a predetermined position in the die opening or closing direction.
This requires a mechanism for moving and positioning the spray head in the die opening/closing directions, and the cost of such a mechanism should necessarily be higher for setting of the spray distance with higher precision. Furthermore, the spray apparatus needs to perform the two-step operation of: moving the spray head in the die opening or closing direction from a stand-by position to position the spray head at an approach start position; and moving the spray head to a position between the fixed die and the movable die. Such a two-step operation has the problem of long cycle time.